Source Apportionment of Exposure to Toxic Volatile Organic CompoundsEPA Grant Number: R826788
Title: Source Apportionment of Exposure to Toxic Volatile Organic Compounds
Institution: University of Colorado at Boulder
EPA Project Officer: Hunt, Sherri
Project Period: October 1, 1998 through September 30, 2000 (Extended to June 30, 2001)
Project Amount: $129,695
RFA: Urban Air Toxics (1998) RFA Text | Recipients Lists
Research Category: Air Quality and Air Toxics , Air
Description:The overall objective of the proposed research is to estimate the contributions that various sources make to human exposure to toxic volatile organic compounds (VOCs), using receptor-oriented source apportionment techniques. The study seeks to distinguish between indoor and outdoor sources of personal exposure, as well as among various indoor and urban area sources. As a preliminary step in the source apportionment procedure, three multivariate techniques for extracting source profiles from exposure data will be tested. An additional objective of the research is to demonstrate methods for evaluating the source apportionment results, using simulated exposure data, and using questionnaire data from personal exposure studies.
Approach:The proposed research will apply receptor-oriented source apportionment techniques to existing measurements of personal exposure to toxic VOCs. The primary source of data will be the U.S. Environmental Protection Agency's Total Exposure Assessment Methodology (TEAM) studies, which measured personal exposures and indoor and outdoor air concentrations of a suite of VOCs. A multi-step process will be used to estimate source contributions. Chemical profiles for key sources will be compiled from the literature. For indoor and personal sources, the published source profiles will be supplemented or refined using multivariate techniques applied to the exposure or indoor air concentration data. Three published methods for extracting profiles will be tested and compared: absolute principal component scores (APCS); graphical ratio analysis for composition estimates/source apportionment by factors with explicit restrictions (GRACE/ SAFER); and positive matrix factorization (PMF). A chemical mass balance (CMB) model will then be used to determine the contributions of individual sources. In parallel with the CMB application, an indoor air mass balance model will also be used to distinguish between contributions from outdoor and indoor sources. Prior to its application to the TEAM data, the source apportionment scheme will be tested using a simulated data set generated with specified source contributions and profiles. Finally, the source apportionment results will be evaluated using questionnaire data from the TEAM studies that indicate the influence of personal and household characteristics.
Source contributions will be estimated for the following 112 HAPs and potential 112(k) HAPs*: benzene*; bromoform; carbon tetrachloride*; chlorobenzene; chloroform*; ethylene dibromide* (1,2-dibromoethane); 1,4-dichlorobenzene*; ethylene dichloride* (1,2-dichloroethane); 1,4-dioxane; ethyl benzene; styrene*;1,1,2,2,-tetrachloroethane; tetrachloroethylene*; 1,1,1-trichloroethane; trichloroethylene*; o-xylene; m-xylene; and p-xylene. In the course of developing these estimates, methods for applying receptor modeling to personal exposure data will be demonstrated. The proposed methods will be applicable in the future for evaluating progress in reducing exposures to toxic VOCs, using up-to-date exposure data such as those that are currently being collected in the National Human Exposure Assessment Survey (NHEXAS), a statistically based national survey of U.S. population exposures.
Improvement in Risk Assessment or Risk Management: Substantial evidence demonstrates that exposure to many toxic volatile organic compounds poses significant health risks. For many of these compounds, little information is available on human exposure levels and information on the relative contributions of the many potential sources is completely lacking. Completion of the proposed research will substantially improve our understanding of the major sources of exposure to toxic VOCs. Such information is needed to devise effective mitigation or control strategies to reduce exposures.